1. Avast makes good stuff
  2. It costs money to develop, maintain and improve good stuff
  3. Avast has a close working relationship with Google.
  4. You get what you pay for. If you want to get rid of the pop-up just buy an avast! Pro or AIS license or find an inferior anti-Virus product that is free and has no pop-ups.

This is not rocket science.

This is life.